High-speed transimpedance amplifier

ABSTRACT

A transimpedance amplifier includes a first inverter having a first input node and a first output node. The first input node is configured to be coupled to an input signal. A second inverter has a second input node and a second output node. The second input node is configured to receive a reference voltage terminal. The first inverter and the second inverter are configured to provide a differential output voltage signal between the first output node and the second output node.

TECHNICAL FIELD

The present disclosure relates generally to an integrated circuit and more particularly to a transimpedance amplifier (TIA).

BACKGROUND

In some applications, an optical link is more energy-efficient than an electrical link for high-speed (e.g., 40 Gbps or higher) input/output traffic. A transimpedance amplifier (TIA) receives a small current signal from a photo detector in an optical receiver and converts it into a voltage signal for the next stage circuit in the optical receiver. A low-power and high-sensitivity TIA is desirable for high-speed optical links. For the TIA, reduction of jitter and generation of a clean eye pattern in the received signal are issues for applications in high-data rates.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary transimpedance amplifier (TIA) in an optical receiver according to some embodiments;

FIG. 2 is a schematic diagram of another exemplary TIA in an optical receiver according to some embodiments;

FIG. 3 is an exemplary circuit diagram of the TIA in FIG. 1 according to some embodiments;

FIG. 4 is an exemplary circuit diagram of the TIA in FIG. 2 according to some embodiments; and

FIG. 5 is a flowchart of a method for operating the exemplary TIA in FIGS. 1-4 according to some embodiments.

DETAILED DESCRIPTION

The making and using of various embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use, and do not limit the scope of the disclosure.

In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a feature on, connected to, and/or coupled to another feature in the present disclosure that follows may include embodiments in which the features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the features, such that the features may not be in direct contact. In addition, spatially relative terms, for example, “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of the present disclosure of one features relationship to another feature. The spatially relative terms are intended to cover different orientations of the device including the features.

FIG. 1 is a schematic diagram of an exemplary transimpedance amplifier (TIA) 102 in an optical receiver 100 according to some embodiments. A portion of an optical receiver 100 in FIG. 1 includes a photo detector 101 and a TIA 102. The TIA 102 includes two inverters 104 a and 104 b, two amplifiers 106 a and 106 b, two resistors R, two inductors L, a capacitor C_(PD), and a current source Ic. The inverters 104 a and 104 b have input nodes 108 a and 108 b and output nodes 110 a and 110 b, respectively.

The input node 108 a of the inverter 104 a is coupled to an input current from the photo detector 101 through one inductor L. The input node 108 b of the inverter 104 b is coupled to a reference voltage terminal (e.g., ground terminal) through another inductor L and the capacitor C_(PD). The two optional inductors L are coupled to the input nodes 108 a and 108 b for inductive peaking (i.e., for increased bandwidth). The inductance values of both inductors L are the same to have a balanced circuit for a differential output voltage signal Vo in some embodiments. The differential output Vo is provided between the output nodes 110 a and 110 b of the inverters 104 a and 104 b.

Amplifiers 106 a and 106 b provide feedback and inverting amplification to the inverter input nodes 108 b and 108 a respectively to have a balanced circuit for the differential output Vo. The amplifier 106 b receives its input from the inverter input node 108 b and provides its output to the input node 108 a of the inverter 104 a, while the amplifier 106 a receives its input from the inverter input node 108 a and provides its output to the input node 108 b of the inverter 104 b.

For example, if the signal at the input node 108 a of the inverter 104 a increases, the signal at the amplifier 106 a also increases and provides decreasing output at the input node 108 b of the inverter 104 b. Thus, the output node 110 b of the inverter 104 b increases. With the input node 108 b of the inverter 104 b decreasing, the amplifier 106 b has its input decreasing and provides its output increasing to the input node 108 a. Thus, the signal at the output node 110 a of the inverter 104 a decreases.

One resistor R is coupled between the input node 108 a and the output node 110 a of the inverter 104 a (i.e., in parallel) and another resistor R is coupled between the input node 108 b and the output node 110 b of the inverter 104 b (i.e., in parallel). The resistors R keep the voltages at the input nodes 108 a and 108 b at a high gain region of the inverters 104 a and 104 b by providing feedback from the output nodes 110 a and 110 b. The resistance values of both resistors R are the same to have a balanced circuit for the differential output Vo. The current source Ic is coupled to both the inverters 104 a and 104 b for regulating electrical current, which improves noise immunity and balance of the differential output voltage Vo by having a common current source Ic. The capacitor C_(PD) coupled between the input node 108 b and the reference voltage terminal (e.g., ground terminal) has an equivalent capacitance of the photo detector 101 to have a balanced circuit in some embodiments.

By having the current source Ic (current tail) and amplifiers 106 a and 106 b, the noise immunity and jitter performance is significantly improved by the TIA 102 in the optical receiver 100. Also, the power consumption is reduced compared to a similar circuit using two current sources instead of one current source Ic.

FIG. 2 is a schematic diagram of another exemplary TIA 202 in an optical receiver 200 according to some embodiments. The TIA 202 is similar to the TIA 102 in FIG. 1, except that the amplifiers 206 a and 206 b provide feedback and non-inverting amplification to the inverter input nodes 108 a and 108 b respectively to have a balanced circuit for the differential output Vo. The amplifier 206 a receives its input from the inverter output node 110 b and provides its output to the input node 108 a of the inverter 104 a, while the amplifier 206 b receives its input from the inverter output node 110 a and provides its output to the input node 108 b of the inverter 104 b.

For example, if the signal at the input node 108 a increases, the signal at the output node 110 a of the inverter 104 a decreases that is input to the amplifier 206 b. The amplifier 206 b provides its output decreasing to the input node 108 b of the inverter 104 b. Thus, the signal at the output node 110 b increases. With the output node 110 b of the inverter 104 b increasing, the amplifier 206 a has its input increasing and provides its output increasing to the input node 108 a of the inverter 104 a. Thus, the output node 110 a of the inverter 104 a decreases.

Similar to the TIA 102, the noise immunity and jitter performance is significantly improved by the TIA 202 in the optical receiver 200. Also, the power consumption is reduced compared to a similar circuit using two current sources instead of one current source Ic.

FIG. 3 is an exemplary circuit diagram of the TIA in FIG. 1 according to some embodiments. The inverter 104 a comprises a PMOS transistor P1 and an NMOS transistor N1. The inverter 104 b comprises a PMOS transistor P3 and an NMOS transistor N3. The amplifier 106 a comprises an NMOS transistor N2 and the amplifier 106 b comprises an NMOS transistor N4. A PMOS transistor P2 is coupled in parallel with a resistor R1 and a PMOS transistor P4 is coupled in parallel with another resistor R1. By adjusting the bias voltage V_(B) of the PMOS transistor P2 or P4, the effective combined resistance R of the resistor R1 and the PMOS transistor P2 or P4 can be changed.

In one example, the TIA 102 in FIG. 3 provided the output voltage Vo with a clean eye pattern and a small jitter of less than 1 ps for a high speed input signal at 40 Gbps, compared to a conventional TIA having a jitter of about 10 ps. The frequency and speed of the TIA 102 is not limited to this example in other embodiments.

FIG. 4 is an exemplary circuit diagram of the TIA in FIG. 2 according to some embodiments. The inverter 104 a comprises a PMOS transistor P1 and an NMOS transistor N1. The inverter 104 b comprises a PMOS transistor P3 and an NMOS transistor N3. The amplifier 206 b comprises a PMOS transistor P5 and the amplifier 206 a comprises a PMOS transistor P6. A PMOS transistor P2 is coupled in parallel with a resistor R2 and a PMOS transistor P4 is coupled in parallel with another resistor R2. By adjusting the bias voltage V_(B) of the PMOS transistor P2 or P4, the effective resistance R can be adjusted. Also, and by adjusting the bias voltage V_(B) of PMOS transistors P4, the effective combined resistance R of the resistor R1 and the PMOS transistor P2 or P4 can be changed.

Similar to the TIA 102 in FIG. 3, the TIA 202 in FIG. 4 provided the output voltage Vo with a clean eye pattern and a small jitter of less than 1 ps for a high speed input signal at 40 Gbps in one example, compared to a conventional TIA having a jitter of about 10 ps. Also, the efficiency in J/bit of the TIA 202 with 62.5 fj/bit, which is improved ten times compared to 625 fj/b of the conventional TIA. The frequency and speed of the TIA 202 is not limited to this example in other embodiments.

FIG. 5 is a flowchart of a method for operating the exemplary TIA in FIGS. 1-4 according to some embodiments. At step 502, a first input node 108 a of a first inverter 104 a receives an input signal from a photo diode 101. At step 504, a second input node 108 b of a second inverter 104 b is coupled to a reference voltage terminal, such as to a ground terminal. At step 506, a differential output voltage signal Vo is provided between a first output node 110 a of the first inverter 104 a and a second output node 110 b of the second inverter 104 b.

In various embodiments, a first amplifier provides feedback to the first input node 108 a and a second amplifier provides feedback to the second input node 108 b. In some embodiments, the first amplifier 106 b receiving a first input from the second input node 108 b to provide inverting amplification to the first input node 108 a. The second amplifier 106 a receives a second input from the first input node 108 a to provide inverting amplification to the second input node 108 b. In some embodiments, the first amplifier 206 a receives a first input from the second output node 110 b to provide non-inverting amplification to the first input node 108 a. The second amplifier 206 b receives a second input from the first output node 110 a to provide non-inverting amplification to the second input node 108 b.

In various embodiments, a first resistor R is coupled between the first input node 108 a and the first output node 110 a. A second resistor R is coupled between the second input node 108 b and the second output node 110 b. A first inductor L is coupled to the first input node 108 a for inductive peaking. A second inductor L is coupled to the second input node 108 b for inductive peaking. A current source Ic coupled to both the first inverter 104 a and the second inverter 104 b for regulating electrical current. A capacitor C_(PD) having an equivalent capacitance of a photo detector 101 is coupled between the second input node 108 b and the reference voltage terminal (e.g., ground terminal).

According to some embodiments, a transimpedance amplifier includes a first inverter having a first input node and a first output node. The first input node is configured to be coupled to an input signal. A second inverter has a second input node and a second output node. The second input node is configured to be coupled to a reference voltage terminal (e.g., ground terminal). The first inverter and the second inverter are configured to provide a differential output voltage signal between the first output node and the second output node.

According to some embodiments, a method for operating a transimpedance amplifier (TIA) includes a first input node of a first inverter receiving an input signal from a photo detector. A second input node of a second inverter is coupled to a reference voltage terminal. A differential output voltage signal is provided between a first output node of the first inverter and a second output node of the second inverter.

A skilled person in the art will appreciate that there can be many embodiment variations of this disclosure. Although the embodiments and their features have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosed embodiments, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure.

The above method embodiment shows exemplary steps, but they are not necessarily required to be performed in the order shown. Steps may be added, replaced, changed order, and/or eliminated as appropriate, in accordance with the spirit and scope of embodiment of the disclosure. Embodiments that combine different claims and/or different embodiments are within the scope of the disclosure and will be apparent to those skilled in the art after reviewing this disclosure. 

What is claimed is:
 1. A transimpedance amplifier (TIA), comprising: a first inverter having a first input node and a first output node, wherein the first input node is configured to receive an input signal and the first output node is directly coupled to the first inverter; a second inverter having a second input node and a second output node, wherein the second input node is configured to be coupled to a reference voltage terminal and the second output node is directly coupled to the second inverter, wherein the first inverter and the second inverter are configured to provide a differential output voltage signal between the first output node and the second output node; and a first amplifier and a second amplifier, wherein the first amplifier and the second amplifier are configured to provide feedback to the first input node and the second input node, respectively.
 2. The TIA of claim 1, wherein the first amplifier is configured to receive a first input from the second input node and provide a first output to the first input node, the second amplifier is configured to receive a second input from the first input node and provide a second output to the second input node, and the first amplifier and the second amplifier are configured to provide inverting amplification.
 3. The TIA of claim 2, wherein the first amplifier comprises a first NMOS transistor and the second amplifier comprises a second NMOS transistor.
 4. The TIA of claim 1, wherein the first amplifier is configured to receive a first input from the second output node and provide a first output to the first input node, the second amplifier is configured to receive a second input from the first output node and provide a second output to the second input node, and the first amplifier and the second amplifier are configured to provide non-inverting amplification.
 5. The TIA of claim 4, wherein the first amplifier comprises a first PMOS transistor and the second amplifier comprises a second PMOS transistor.
 6. The TIA of claim 1, further comprising a first resistor coupled between the first input node and the first output node and a second resistor coupled between the second input node and the second output node.
 7. The TIA of claim 1, further comprising a first inductor coupled to the first input node and a second inductor coupled to the second input node for inductive peaking.
 8. The TIA of claim 1, further comprising a current source coupled to both the first inverter and the second inverter for regulating electrical current.
 9. The TIA of claim 1, wherein the reference voltage terminal is a ground terminal.
 10. The TIA of claim 9, further comprising a capacitor coupled between the second input node and the ground terminal.
 11. The TIA of claim 10, wherein the capacitor has an equivalent capacitance of a photo detector coupled to the first input node.
 12. The TIA of claim 6, further comprising a first PMOS transistor configured in parallel with the first resistor and a second PMOS transistor configured in parallel with the second resistor.
 13. A method for operating a transimpedance amplifier (TIA), comprising: a first input node of a first inverter receiving an input signal from a photo detector; coupling a second input node of a second inverter to a ground terminal; providing a differential output voltage signal between a first output node directly coupled to the first inverter and a second output node directly coupled to the second inverter; a first amplifier providing feedback to the first input node; and a second amplifier providing feedback to the second input node.
 14. The method of claim 13, further comprising: the first amplifier receiving a first input from the second input node to provide inverting amplification to the first input node; and the second amplifier receiving a second input from the first input node to provide inverting amplification to the second input node.
 15. The method of claim 13, further comprising: the first amplifier receiving a first input from the second output node to provide non-inverting amplification to the first input node; and the second amplifier receiving a second input from the first output node to provide non-inverting amplification to the second input node.
 16. The method of claim 13, further comprising: coupling a first inductor to the first input node for inductive peaking; and coupling a second inductor to the second input node for inductive peaking.
 17. The method of claim 13, further comprising coupling a current source coupled to both the first inverter and the second inverter for regulating electrical current.
 18. The method of claim 13, further comprising coupling a capacitor having an equivalent capacitance of a photo detector between the second input node and the ground terminal.
 19. The method of claim 13, further comprising coupling a first adjustable resistance between the first input node and the first output node and a second adjustable resistance between the second input node and the second output node.
 20. An optical receiver, comprising: a photo detector; and a transimpedance amplifier, comprising: a first inverter having a first input node and a first output node, wherein the first input node is configured to receive an input signal from the photo detector; a capacitor coupled to a ground terminal, the capacitor having an equivalent capacitance of the photo detector; a second inverter having a second input node and a second output node, wherein the second input node is configured to be coupled to the capacitor; a first amplifier configured to provide feedback to the first input node; a second amplifier configured to provide feedback to the second input node; a first resistor coupled between the first input node and the first output node; a second resistor coupled between the second input node and the second output node; a first inductor coupled to the first input node for inductive peaking; a second inductor coupled to the second input node for inductive peaking; and a current source coupled to both the first inverter and the second inverter for regulating electrical current; wherein the first inverter and the second inverter are configured to provide a differential output voltage signal between the first output node and the second output node. 